The present invention relates to a fuel control apparatus in a car internal combustion engine, and particularly relates to a fuel control apparatus which is suitable to obtain an optimum air-fuel ratio (hereinafter simply abbreviated to "A/F") in acceleration again through deceleration after acceleration.
Generally, an air flow rate changes in proportion to the opening of a throttle valve. However, even if the throttle valve is fully closed from a fully opened state, air flow cannot immediately respond to the closure of the throttle valve but responds with a temporal delay.
This is because a suction air path has a length to the throttle valve and an air flow rate sensor is provided upstream the throttle valve. Accordingly, in spite of the fact that the value A/F should be made rich when the throttle valve is moved toward the open side, that is, when the engine is accelerated, the value of A/F can not be made so rich as to sufficiently accelerate the engine even if an optimum fuel supply quantity calculated on the basis of the suction air quantity detected by the air flow rate sensor is injected through a fuel injector. Therefore, the control delay due to determination of the fuel supply quantity by means of the air flow rate sensor has been conventionally corrected by increasing the opening of the throttle valve.
Conventionally, in a system in which acceleration correction is performed by using a throttle sensor as disclosed in Japanese patent unexamined publication No. 58-185949, so-called constant acceleration correction in which a quantity of change per predetermined unit time, that is, a quantity of differentiation, of an output of the throttle sensor is detected, and the fuel supply quantity calculated on the basis of the suction air quantity detected by the air flow rate sensor is multiplied by a certain factor (for example, 1.1) to thereby increase the fuel supply quantity when the change of rate of the output of the throttle sensor exceeds a predetermined value.
Thus, in the conventional acceleration corection, even in the case where after acceleration, deceleration is once performed for a short time and then acceleration is to be made again, the fuel supply is increased by the same quantity as in the first acceleration. However, the whole of the increased fuel injected upstream the throttle valve is not evaporated so as to be sucked into a cylinder, but some of the fuel is liquefied and adheres to the side wall of the carburetor. Accordingly, if the fuel supply is increased by the same quantity as in the first time acceleration when acceleration is to be made again after deceleration is made once after the first time acceleration, the fuel becomes so rich disadvantageously that not only the fuel consumption rate becomes poor but complete combustion cannot be obtained and exhaust gas characteristics becomes poor.
Gasoline atomized in the vicinity of the throttle chamber is used to wet a collector by a quantity of several percent and the remainder quantity of the gasoline is sucked into the engine through an intake manifold.
On the contrary, the adhering gasoline is evaporated by several percent of the whole quantity thereof and sucked into the engine together with the atomized gasoline so as to contribute to the combustion. Accordingly, when the engine is in a steady state, the whole quantity of adhering gasoline is constant and is called an equilibrated adhering quantity (hereinafter simply referred to "MFH"). The MFH is a function of a water temperature and a load (it may be considered as a negative pressure quantity), so that the MFH is large when the engine output is high, while small when the engine output is low. When acceleration is made by increasing the opening of a throttle, gasoline is used for filling the quantity of increase of the MFH even if the gasoline is injected by a quantity corresponding to the suction air quantity, so that the air-fuel mixture actually sucked into the engine becomes lean. To correct this state, the quantity of fuel injection is increased by a little quantity. This acceleration is called "increased-fuel acceleration".